1. Field of the Invention
The present invention relates to curable resinous compositions and more particularly relates to curable resinous coating compositions in which the resinous binder cures via a Michael addition reaction.
2. Brief Description of the Prior Art
Resinous coating compositions which cure via a Michael addition reaction are known in the art. Thus, for example, U.S. Pat. No. 3,975,251 to McGinniss discloses cationic electrodepositable compositions comprising an acid-solubilized polyamine resin in combination with polyacrylate curing agents. Upon electrodeposition, the polyamine resin deprotonates exposing primary or secondary amine groups which react via a Michael addition with the polyacrylate to form a cured coating on the cathode.
In such compositions, it is necessary that the polyamine resins be completely neutralized (100 percent or more of the total theoretical neutralization) in order to prevent any premature reaction between an unprotonated polyamine resin and the polyacrylate curing agent in the electrodeposition bath.
The present invention is an improvement over the compositions of U.S. Pat. No. 3,975,251. In the present invention, the alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties are reacted with a primary and/or secondary amine which is volatile under curing conditions. Thus, any premature reaction before cure of the alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties is avoided. When the compositions are heated to curing temperatures, it is believed the adduct decomposes releasing amine which volatilizes generating alpha, beta-ethylenically unsaturated carbonyls which cure via a Michael addition reaction with non-volatile primary and/or secondary amines present in the composition.
Reference is also made to application Ser. No. 937,386, filed Aug. 28, 1978, entitled "Michael Adducts of Polymeric Materials Useful in Coating Applications". This application relates to resinous coating compositions dispersible in aqueous medium with the aid of cationic salt groups and aqueous dispersions of such resinous coating compositions. The resinous coating composition comprises as the resinous binder:
(A) a polymeric material containing alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties selected from the class consisting of ##STR1## reacted under conditions sufficient to form a Michael adduct with (B) a primary and/or secondary amine which has a boiling point below 200.degree. C.; PA0 (A) a polyamine resin containing primary and/or secondary amino groups, said polyamine resin being stable under curing conditions; and PA0 (B) a Michael adduct of an organic material containing alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties reacted with primary and/or secondary amines, said Michael adduct being unstable under curing conditions;
said reaction product of (A) and (B) being at least partially neutralized with acid to provide cationic salt groups; said coating composition being electrodepositable on a substrate to form a film thereon.
Reference is also made to application Ser. No. 180,742, filed Aug. 25, 1980, which is a division of application Ser. No. 937,386, and which relates to a method of cationic electrodeposition employing the resinous compositions disclosed in application Ser. No. 937,386.
The present invention relates to a method of coating an electrically conductive surface serving as a cathode which comprises passing electric current between said cathode and an anode immersed in an aqueous dispersion of an electrodepositable curable resinous composition, comprising as the resinous binder:
said resinous binder being neutralized with acid to provide cationic salt groups. When heated to curing temperatures, the film cures via what is believed to be a Michael exchange, that is, the Michael adduct (B) decomposes releasing amine and generating alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties. The film crosslinks via reaction of the non-volatile amino groups in (A) and the generated alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties in (B).
Besides being in the form of two-component systems in which the stable polyamine resin and the unstable Michael adduct are present as separate components, the resinous composition can also be in the form of a one-component system in which non-volatile and volatile amines are in the same polymer molecule.
The resinous compositions of the present invention are desirable as aqueous-based compositions in which at least part of the amine groups are converted to cationic groups by the addition of acid. Such compositions can be used for cationic electrodeposition.